U.S. patent application number 13/833856 was filed with the patent office on 2013-11-14 for method and apparatus for 3d orientation-free wireless power transfer.
This patent application is currently assigned to SAMSUNG ELECTRONICS CO., LTD.. The applicant listed for this patent is SAMSUNG ELECTRONICS CO., LTD.. Invention is credited to Farshid Aryanfar, Sridhar Rajagopal, Ioannis Tzanidis.
Application Number | 20130300205 13/833856 |
Document ID | / |
Family ID | 49548086 |
Filed Date | 2013-11-14 |
United States Patent
Application |
20130300205 |
Kind Code |
A1 |
Tzanidis; Ioannis ; et
al. |
November 14, 2013 |
METHOD AND APPARATUS FOR 3D ORIENTATION-FREE WIRELESS POWER
TRANSFER
Abstract
A transmit resonator includes at least two loop resonators,
disposed in such that the magnetic field produced by each in the
near-field zone is substantially orthogonal to that produced by the
other at a certain or specific portion of the zone, a power divider
configured to split a signal into at least two sub-signals with
weighting coefficients, a delay array configured to delay the at
least one of the sub-signals and feed each of the sub-signals to
each of the loop resonators, and a controller to configure the
delay array to control the polarization of the near zone magnetic
field. A communication module to receive feedback information from
a receiver, to determine the phases of at least two sub-signals to
generate a near zone magnetic field optimized for the receiver.
Inventors: |
Tzanidis; Ioannis; (Plano,
TX) ; Rajagopal; Sridhar; (Plano, TX) ;
Aryanfar; Farshid; (Allen, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SAMSUNG ELECTRONICS CO., LTD. |
Gyeonggi-do |
|
KR |
|
|
Assignee: |
SAMSUNG ELECTRONICS CO.,
LTD.
Gyeonggi-do
KR
|
Family ID: |
49548086 |
Appl. No.: |
13/833856 |
Filed: |
March 15, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61644943 |
May 9, 2012 |
|
|
|
Current U.S.
Class: |
307/104 |
Current CPC
Class: |
H02J 7/025 20130101;
H04B 5/0087 20130101; H02J 5/005 20130101; H04B 5/0037 20130101;
H02J 50/12 20160201 |
Class at
Publication: |
307/104 |
International
Class: |
H04B 5/00 20060101
H04B005/00 |
Claims
1. An apparatus, comprising: a transmit resonator array including
at least two loop resonators configured to generate a non-radiative
magnetic field in the near-field zone, the at least two loop
resonators disposed such that the magnetic field produced by each
in the near-field zone, is substantially orthogonal to that
produced by the other at a certain or specific portion of the zone;
and a power divider configured to split a signal into at least two
sub-signals being fed to the at least two loop resonators, with
weighting coefficients.
2. The apparatus of claim 1, further comprising: at least one phase
shifter configured to shift phase of the at least one of the at
least two sub-signals with respect to the phase of the other of the
at least two sub-signals.
3. The apparatus of claim 2, further comprising: a controller
configured to control polarization of the near magnetic field by
configuring the power divider and the at least one phase shifter,
to adjust the weighing coefficients and the phases of each
sub-signal, respectively.
4. The apparatus of claim 3, wherein the controller is configured
to set weighting coefficients to be un-equal and set a phase
difference between the at least two resonators to be neither an odd
multiple of 90.degree. nor an multiple of 180.degree., so that the
near zone magnetic field is elliptically polarized in a specific
portion of space surrounding the at least two loop resonators.
5. The apparatus of claim 3, where the controller is configured to
set the weighting coefficients to be equal and phase difference
between the at least two resonators to be odd multiple of
90.degree., so that the near zone magnetic field is circularly
polarized in a specific portion of space surrounding the at least
two loop resonators.
6. The apparatus of claim 3, where the controller is configured to
set the weighting coefficients to be equal and the phase difference
between the at least two resonators to be multiple of 180.degree.,
so that the near zone magnetic field is linearly polarized in a
specific portion of space surrounding the at least two loop
resonators.
7. The apparatus of claim 3, further comprising: a communication
module to receive feedback information from a receiver, to
determine the amplitudes and the phases of at least two sub-signals
to generate the near zone magnetic field optimized to the
receiver.
8. The apparatus of claim 1, wherein the at least two loop
resonators are either separated from one another or overlaid on
portions of one another.
9. The apparatus of claim 1, further comprising: an intermediate
loop resonator configured to relay the near zone magnetic field at
longer ranges.
10. An apparatus, comprising: a receive resonator array including
at least two loop resonators configured to resonate in the presence
of an external non-radiative magnetic field, the at least two loop
resonators being disposed in such that the magnetic field received
by each is substantially orthogonal to that received by the other;
and a power combiner configured to combine sub-signals received
from the at least two loop resonators.
11. The apparatus of claim 10, further comprising: at least one
phase shifter configured to shift phase of one of at least two
sub-signals received by the at least two loop resonators, with
respect to the other.
12. The apparatus of claim 10, further comprising a controller
configured to adjust the phase shifts of the received sub-signals
to optimize the combined reception of power by the at least two
loop resonators.
13. The apparatus of claim 10, further comprising: a communication
module configured to transmit feedback information to a
transmitter, to determine amplitudes and phases of the transmitter
to optimize the near zone magnetic field.
14. The apparatus of claim 10, further comprising: a controller
configured to set a phase difference between the at least two
resonators to be neither an odd multiple of 90.degree. nor an
multiple of 180.degree., so that the at least two loop resonators
receive the sub-signals in an elliptically polarized near zone
magnetic field.
15. The apparatus of claim 10, further comprising: a controller
configured to set a phase difference between the at least two
sub-signals received from the at least two resonators to be an odd
multiple of 90.degree., so that the at least two loop resonators
are configured to optimally receive the sub-signals in a circularly
polarized near zone magnetic field.
16. The apparatus of claim 10, further comprising: a controller
configured to set a phase difference between at least two
sub-signals received from at least two loop resonators to be a
multiple of 180.degree., so that the at least two loop resonators
are configured to optimally receive in a linearly polarized near
zone magnetic field.
17. The apparatus of claim 10, further comprising: a converter
configured to convert the combined signal to DC power and to output
the converted DC power either to charge a battery or to power a
device.
18. The apparatus of claim 10, wherein the at least two loop
resonators are either separated from one another or overlaid on
portions of one another.
19. The apparatus of claim 10, wherein the phase shifts of each
sub-signal are predetermined with respect to the polarization of
the near zone magnetic field.
20. A method, comprising: generating, with at least two loop
resonators, a non-radiative magnetic field in the near-field zone,
the at least two loop resonators disposed in such that the magnetic
field produced by each is substantially orthogonal to that produced
by the other at a certain or specific portion of the zone; shifting
phases of the signals in the at least one of the two loop
resonators in order to optimize the received power with respect to
polarization of the near zone magnetic field; and combining
sub-signals generated from the at least two loop resonators.
21. The method of claim 20, further comprising: transmitting
feedback information to a transmitter to determine phases of the
transmitter's sub-signals to generate the near zone magnetic field
to be optimally received by a receiver.
Description
[0001] This application incorporates by reference the content of
U.S. Provisional Patent Application Ser. No. 61/644, 943, filed May
9, 2012, entitled "METHOD AND APPARATUS FOR ENABLING ORIENTATION
FREE WIRELESS POWER TRANSFER." The content of the above-identified
patent documents is incorporated herein by reference.
TECHNICAL FIELD
[0002] The present disclosure relates to wireless power transfer
systems using magnetic resonance.
BACKGROUND
[0003] Wireless power transfer, also referred to as wireless energy
transfer or wireless charging, to electronic devices is becoming a
global standard. The benefits of wireless power transfer (WPT)
compared to wired power transfer can be summarized as follows:
[0004] Convenience: Users should not need to carry multiple wired
chargers with them to charge devices such as laptops, mobile
phones, tablets, notebooks, and the like. Instead, a wireless
charger can be placed in areas such as conference rooms, coffee
shop tables, airport waiting areas, at home, and so forth, and
users can charge their electronic devices by simply placing the
device close to a wireless charger, without having to use a wired
connection. Standardization of the WPT systems will allow for
charging of multiple devices, possibly of different make and model,
from the same wireless charger, leading to a universal charging
standard.
[0005] Practicality: The number of physical power outlets available
in areas such as conference rooms, coffee shops, airport waiting
areas, and the like is limited, thus restricting the number of
users that have access to them. A wireless power transfer system
overcomes this issue and offers fast and easy charging to multiple
users simultaneously.
[0006] Transparency: Wireless power can penetrate various objects
such as wood, plastic, paper and cloth, making power transfer
possible to locations where physical wire access is either not
recommended or impossible, such as implant devices, under water,
moving while charging, and the like.
[0007] Green: Wireless power transfer is in accordance with the
Universal Charging Solution (UCS) proposed by the International
Telecommunication Union, a United Nations branch. In essence, UCS
recommends the same charger to be used for all future handsets,
regardless of make and model, yielding a 50 percent reduction in
standby energy consumption, elimination of 51,000 tons of redundant
chargers, and a subsequent reduction of 13.6 million tons in
greenhouse gas emissions each year (source: the website of
International Telecommunication Union).
SUMMARY
[0008] An apparatus is provided. The apparatus includes a transmit
resonator including at least two loop resonators that generate a
magnetic field in the near-field zone (non-radiative), the at least
two loop resonators being disposed in such that the magnetic field
produced by each is substantially orthogonal to that produced by
the other at a certain or specific portion of the zone.
Specifically, the at least two loop resonators are oriented
substantially perpendicular to each other. The apparatus also
includes a power divider configured to split a signal into at least
two sub-signals fed to the at least two resonators with amplitude
weighting coefficients.
[0009] Another apparatus is provided. The apparatus includes a
receiver resonator including at least two loop resonators capable
of resonating in the presence of an external non-radiative magnetic
field, the at least two loop resonators being disposed in such that
the magnetic field received by each is substantially orthogonal to
that received by the other. Specifically, the at least two loop
resonators are oriented substantially perpendicular to each other.
A power combiner is configured to combine sub-signals received from
the at least two loop resonators.
[0010] A method is provided. The method includes controlling the
polarization of a magnetic field in the near-field zone, by
shifting phases of the signals in at least one of the two loop
resonators, in order to optimize the received power with respect to
polarization of the generated magnetic field in the near-field
zone. The method further includes combining sub-signals generated
from the at least two loop resonators.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] For a more complete understanding of the present disclosure
and its advantages, reference is now made to the following
description taken in conjunction with the accompanying drawings, in
which like reference numerals represent like parts:
[0012] FIGS. 1A and 1B illustrate mutual inductance between two
loops as a function of the angle of rotation, .phi., of the Rx loop
around its center;
[0013] FIG. 2 illustrates a block diagram for the wireless power
transmission system according to embodiments of the present
disclosure;
[0014] FIG. 3 illustrates a transmitter and a receiver operating
under the linear polarization mode according to embodiments of the
present disclosure;
[0015] FIG. 4 depicts how the linearly polarized magnetic field
oscillates with time on a straight line but at different
orientations depending on the location in the space around the
resonator;
[0016] FIG. 5 illustrates a transmitter and a receiver operating
under the elliptical polarization mode according to embodiments of
the present disclosure;
[0017] FIG. 6 depicts the ellipse traced by the tip of the field
vector at a fixed location in space, say r=r0, in the elliptical
polarization mode according to embodiments of the present
disclosure;
[0018] FIG. 7 illustrates a resonator array according to
embodiments of the present disclosure;
[0019] FIG. 8 illustrates exemplary phase shift circuits for time
delay excitation according to embodiments of the present
disclosure;
[0020] FIG. 9 illustrates a wireless transfer system using a
transmit and receive resonators according to embodiment of the
present disclosure; and
[0021] FIG. 10 depicts the mutual inductance M of the system of
resonators with and without the use of phase shifters according to
embodiments of the present disclosure.
DETAILED DESCRIPTION
[0022] FIGS. 1 through 10, discussed below, and the various
embodiments used to describe the principles of the present
disclosure in this patent document are by way of illustration only
and should not be construed in any way to limit the scope of the
disclosure. Those skilled in the art will understand that the
principles of the present disclosure may be implemented in any
suitably arranged wireless power transfer system.
Inductive and Capacitive Coupling Techniques
[0023] U.S. Pat. No. 2,133,494 issued to Water introduced inductive
coupling technique for wireless power transfer, where based on
Faraday's and Ampere's laws, energy was transferred via mutual
induction between two planar or 3D coils, one placed at the
transmitting device and the other at the receiving device. This
technique has been widely used ever since in house appliances, such
as cooking utensils, water heaters, electric toothbrushes, table
lamps, and more recently for charging cell phones. See, for
example, U.S. patent application Ser. No. 12/472,337 naming
Randall, et al. as the inventors. Although wireless in nature,
inductive coupling is only efficient at trivial distances (less
than a few mm), which for most applications implies direct contact
of the transmitter and receiver devices. Another drawback of
inductive coupling is that it requires a very precise alignment
between the coils of the transmitter and the receiver devices,
assisted in some cases by magnets. To address this issue, U.S. Pat.
No. 7,952,322 to Partovi, et al. demonstrates a technique where the
transmitter surface is divided up into many small coils that can be
selectively switched on and off, depending on the receiver's
position on the pad, thus providing an effectively larger charging
area with more uniform magnetic flux than that of a single coil
that covers the same physical area. Instead of inductive coupling,
power transfer can be achieved by means of capacitive coupling.
See, for example, U.S. patent application Ser. No. 12/245,460
naming Bonin as an inventor.
Resonant Coupling Techniques
[0024] In 2007, Karalis et al. ("Efficient wireless non-radiative
mid-range energy transfer", Ann. Physics, 2007), demonstrated
another wireless power transfer technique, referred to as
"non-radiative midrange energy transfer", which enabled power
transfer to distances ranging from a few centimeters to a few
meters. This technique was based on resonant coupling, described by
the coupled mode theory (Haus et al., "Coupled mode theory", 1991).
Resonant coupling works in principle as follows: two objects placed
at each other's near-field (non-radiative field) tend to couple
energy to each other efficiently if their resonance frequency is
the same, but inefficiently if their resonance frequency is not the
same. A key feature of resonant coupling is that high coupling
efficiency is associated with resonators with high quality factors.
U.S. patent application Ser. No. 12/789,611 naming Campanella et
al. as the inventors shows a generic example of two coupled
resonators, separated by distance D. The first resonator designated
as source is connected to a power supply, and the second resonator
is connected to a load designated as device, which consumes or
stores the power coupled to it by the source. An example of two
such resonators is the ring shaped resonators as shown in FIG. 8 of
U.S. patent application Ser. No. 12/789,611.
[0025] The operation principle of resonant coupling implies the
following:
[0026] 1) Energy is exchanged not by radiation, but by the
non-radiative reactive near field. Thus, the resonating objects are
placed within each other's near field zone. This implies that the
operating wavelength is much larger than the physical sizes of the
resonators, i.e. the resonators are electrically small objects.
[0027] 2) Electrically small objects behave generally either as
inductors (small loops) or capacitors (small dipoles), and are
inherently non-resonant, unless they are forced to resonate by
means of adding a capacitance or inductance, respectively, in
series or in parallel to their terminals. In the case of inductive
resonators, coupling occurs via mutual inductance, whereas in the
case of capacitive resonators, coupling occurs via mutual
capacitance. An example of inductively coupled resonators is
described in U.S. Pat. No. 7,825,543 to Karalis et al. Coupling
occurs via mutual inductance M between inductors Ls and Ld, while
the capacitors Cs and Cd are used to resonate the structure at the
desired frequency.
[0028] 3) Coupling efficiency is proportional to the quality factor
Q of the resonators. The quality factor of a resonator is defined
as the ratio of its reactance (capability to store energy in the
near field) over its resistance (dissipated energy or loss). In
electrically small objects, resistance is mainly due to dielectric
or Ohmic losses, and less due to radiation loss, which is generally
negligible. Efficient wireless power transfer requires high Q
resonators, and as such is susceptible to even small amounts of
loss. To reduce the amount of loss, a technique was recently
proposed based on using superconducting materials and low loss
dielectric-less capacitors. See, for example, U.S. patent
application Ser. No. 13/151,020 naming Sedwick as the inventor.
Improving Efficiency in Mutual Coupling
[0029] As mentioned above, coupling efficiency is maximized at the
resonance frequency of the employed resonators. This frequency is
determined by the size and shape of the resonators, which can be
precisely tuned by a capacitor (or inductor in case of capacitive
mutual resonant coupling) connected in series or in parallel to
their terminals. The value of this tuning element is a function of
the desired resonance frequency and also the equivalent electrical
parameters (R, L, C and M) of the coupled resonators. Referring now
to FIG. 10 of U.S. Pat. No. 7,825,543 to Karalis et al., for
example, source-side capacitance C.sub.s and drain-side capacitance
C.sub.d would be determined by source-side inductance L.sub.s,
drain-side inductance L.sub.d, and the desired resonance frequency.
Further, the parameters L.sub.s, L.sub.d and M are a function of
the resonators shape, size and most importantly the relative
position of the involved resonators.
[0030] In various practical applications, such as cell phone
charging, the receiver device can change position during charging,
causing the circuit parameters L.sub.s, L.sub.d and primarily M to
change accordingly. Although L.sub.s, L.sub.d are affected little
by motion or rotation of the receiver resonator, mutual inductance
M changes significantly, leading to frequency detuning and dramatic
drop in the power transfer efficiency. This is one of the biggest
challenges of the resonant coupling technique.
[0031] U.S. patent application Ser. No. 12/789,611 naming to
Gampanellar as the inventors introduces an adaptive matching
network as a solution to the detuning problem. As shown in FIG. 2
of the application, changes in mutual inductance M detune the
resonance frequency, which is re-tuned by a variable capacitor
C.sub.1. However, depending on the use case, implementing an
adaptive tuning network can increase the system complexity and cost
significantly. Often, to ensure fast and efficient tuning of the
coupled resonators, the transmitter and receiver communicate via a
wireless channel (e.g., Zigbee). This configuration is referred to
as "closed loop", vs. the "open loop" where the transmitter or
receiver has to find the optimum tuning setting independently, for
example by minimizing some metric such as the VSWR on their feed
lines as described in U.S. patent application Ser. No. 12/266,522
naming Toncich as the inventor.
[0032] Changes in the coupling condition that lead to detuning
occur not only when one of the resonators changes position. In a
scenario of multiple resonators, when resonators are added to or
removed from the wireless charging network, detuning may occur. In
these cases, besides retuning, other considerations in the system
level become very important for maintaining high efficiency, such
as power distribution and management between multiple receivers
(U.S. patent application Ser. Nos. 12/249,861 and 12/720,866).
Further, to selectively transfer power to certain devices and
prevent power transfer to unauthorized ones, a technique was
proposed based on frequency hopping (U.S. patent application Ser.
No. 12/651,005)
Randomly Oriented Receivers and Longer Range Power Transfer
[0033] To increase the range of wireless power transfer, U.S.
patent application Ser. Nos. 12/323,479 and 12/720,866 proposed a
technique using intermediate resonators (referred to as repeaters)
to transfer power to more distance resonators. In a room
environment, this concept can be applied as shown in FIG. 12. A
large loop (referred to as "long range room antenna") enclosing the
whole room is connected to a generator. To increase the efficiency
of power transfer to multiple devices, the repeater loops P.sub.1
and P.sub.2 are employed.
[0034] Another technique for increasing the range of wireless power
transfer is to use the so called "near field focusing" technique,
introduced by R. Merlin (see, R. Merlin, "Radiationless
Electromagnetic Interference Evanescent-Field Lenses and Perfect
Focusing", 10.1126/science.1143884) and A. Grbic (A. Grbic,
"Near-field focusing plates and their design", IEEE Trans. On
Antennas and Propagation, Vol. 36, Issue 10, pp 3159-3165, 2008).
Near-field focusing was proposed in U.S. patent application Ser.
No. 12/978,553 naming Ryu et al. as the inventors via a
metasuperstrate, MNZ/ENZ (p near zero/E near zero) material, or
high impedance surface (HIS). The metasuperstrate is placed in
front of the transmit resonator and can focus its near-field at the
location of the receive resonator, with subwavelength accuracy.
[0035] A technique for transferring power to randomly oriented
receivers is described in U.S. patent application Ser. No.
12/053,542 naming Ryu et al. as the inventors. Referring now to
FIG. 4, the transmit resonator is mounted on a pillar or bar and
vertically placed on a flat surface. The transmit resonator
transfers energy wirelessly to the receive resonators embedded in
the frames of the 3D glasses lying on the flat surface. Similarly,
a technique based on using orthogonally placed resonators, such as
loops, for charging power tools in metallic cabinets or portable
tool cases is described in U.S. patent application Ser. No.
12/567,339 naming Ozaki et al. as the inventors. Orthogonal
placement of the transmit resonators on the side walls and
top/bottom of the cabinet or tool case, was claimed to provide for
multi-dimensional wireless charging.
Summary of Mutual Inductance Theory
[0036] Power transfer efficiency of wireless power transfer (WPT)
systems depends strongly on the relative position and orientation
of Transmitter (Tx) and Receiver (Rx) units, as well as the
presence of adjacent objects, either participating in the WPT as
repeaters, or not (i.e., extraneous objects) and multiple Rx units.
This is because the mutual coupling measured by the mutual
inductance M between Tx and Rx units changes significantly if the
Rx or Tx units are moved or rotated with respect to each other. In
theory, mutual inductance M.sub.ij between two loops i and j, is
calculated generally by the following equation:
M ij = .PHI. i I j = .intg. S i B .fwdarw. j d .fwdarw. s i I j = V
i I j ( 1 ) ##EQU00001##
where, M.sub.ij is mutual inductance between two loops i and j, and
.PHI..sub.i is magnetic flux through loop i, and I.sub.j is current
of loop j. The flux .PHI..sub.i is due to the magnetic field
intensity B.sub.j caused by the current I.sub.j of loop j.
[0037] Referring to FIG. 1A, where two loops i and j are of a small
size with respect to the operating wavelength, and under the
assumption of a uniform magnetic field B.sub.j produced by current
I.sub.j at the location of loop i, the equation 1 can be simplified
as follows:
M ij = B j A i cos .phi. I j .apprxeq. M 0 cos .phi. ( 2 )
##EQU00002##
where, A.sub.i is the physical area of loop i and cos .phi. is the
angle between the magnetic field vector B.sub.j and the surface
normal of loop i.
[0038] FIG. 1B depicts a typical variation of mutual inductance M
between two loops at a small size with respect to the operating
wavelength, as a function of the angle of rotation, .phi., of one
loop around its center. The solid line comes from numerically
simulated data. The dashed line is the cosine function (see,
Equation 2) fitted to the simulated data. As seen, maximum mutual
inductance of (-)7 nH occurs when the Rx loop is rotated to
.phi.=25.degree.. The minus sign shows that the induced voltage
(electromotive force, EMF) to the Rx reverses polarity. This
behavior is typical in wireless power transfer systems that employ
transmit and receive resonators that are linearly polarized. Such
fluctuations in mutual inductance cause the resonant coupling to
detune and result in severe drops of the power transfer efficiency.
As a result, the Tx unit becomes impedance mismatched, charging of
the Rx unit slows down, or even stops and the Tx unit can suffer
from overheating.
Wireless Power Transmission System
[0039] FIG. 2 illustrates a block diagram for the wireless power
transmission system according to the embodiments of the present
disclosure. The wireless power transmission system includes a
transmitter 10 and a receiver 20, and a near zone magnetic field 30
is formed between the transmitter 10 and the receiver 20. Energy is
transferred from the transmitter to the receiver via the near
magnetic field, which is maximized during matched or nearly matched
resonance between the transmitter 10 and the receiver 20.
[0040] The transmitter can include a power source 11, an oscillator
12, a power amplifier 14, a matching circuit 15, a power divider
16, a delay array, and a transmit (Tx) resonator array 18. The
delay array can be implemented by a phase shifter 17. The
oscillator 12 generates a signal with a desired frequency that is
amplified by the power amplifier 14. The power divider 16 splits
the amplified signal into a number of "M" (#M) sub-signals with the
weighing coefficients A.sub.1, . . . , A.sub.M.
[0041] The divided #M sub-signals are inputted to the delay array,
which can be implemented by a phase shifter 17 that delays the
sub-signals or shifts the #M sub-signals to have the phases
.theta..sub.1, . . . , .theta..sub.M with respect to a reference.
One of these phases can serve as the reference phase, i.e. zero, so
that all other phases can be set with respect the reference phase.
Finally, the Tx resonator array 18 is fed with #M sub-signals with
the weighing coefficients A.sub.1, . . . , A.sub.M and the phases
.theta..sub.1, . . . , .theta..sub.M. The phase shifter 17 can be
designed as part of the feed network, but also structurally
integrated with the resonators (e.g., with surface mount
components).
[0042] The Tx resonator array 18 can include #M resonators
configured such that each produces magnetic fields substantially
orthogonal to the magnetic fields of the others. In one embodiment,
#M resonators can be substantially orthogonal to one another. The
i-th resonator of #M resonators is fed with the i-th sub-signal
with the weighing coefficient A.sub.i and phase .theta..sub.i. Then
the i-th resonator resonates, producing the i-th polarized magnetic
field corresponding to the fed i-th sub-signal. Finally, the first
to M-th magnetic fields generated from #M resonators are combined,
forming a magnetic near field. The matching circuit 15 matches the
internal impedance of the power amplifier to the input impedance of
the combined signal that goes into the Tx resonator array 18.
[0043] The term "substantially orthogonal" as herein to describe
the direction of the magnetic fields, refers to the state that the
direction of vectors of the magnetic fields generated by at least
two loop resonators cross one another to generate a polarized
magnetic field, such as an elliptically, circularly or linearly
polarized magnetic field. The range of degrees between two magnetic
field vector directions in order to be "substantially orthogonal"
is from 15.degree. to 165.degree..
[0044] In some embodiments, the transmitter 10 includes a
communication module to receive feedback information from the
receiver 20, and configures the delays or phases of the sub-signals
of the transmitter 10 to configure the polarization of the
generated near zone magnetic field 30 so that it is optimized for
the receiver 20.
[0045] The receiver 20 resonates in the presence of the magnetic
field 30 to receive power, and charges a battery or powers a device
coupled to the receiver 10. To do this, the receiver 10 can include
a receive (Rx) resonator array 21, a phase shifter 22, a power
combiner 23, a rectifier 26 and a matching circuit 25.
[0046] The Rx resonator array 21 can be comprised of a number of
"N" (#N) resonators that are tuned to have a resonance in presence
of an external magnetic field. The sub-signals induced in each
resonator are delayed appropriately (e.g., by changing their phase
.phi..sub.1, . . . , .phi..sub.N by the phase shifter 22). The i-th
resonator with phase .phi..sub.i is resonated to a portion of the
polarized magnetic field 30 and produces a coupling current from
the resonance. A delay array such as a phase shifter can be
designed as part of the feed network, but also structurally
integrated with the resonators (e.g., surface mount components). As
stated, phase shifter 22 provides each resonator with the
appropriate time delay or phase at the transmitter 10 and receiver
20 respectively.
[0047] The power combiner 23 combines the unequally delayed AC
currents created from the Rx resonator array 21 and the delay
array. By appropriately choosing the sub-signal delays or phases
the power of the combined AC signal can be maximized. This can be
done in conjunction with optimizing the delays or phases of the
sub-signals in the transmitter array. The rectifier 26 converts the
combined AC current to the DC current which is stored or consumed
by a device. The matching circuit matches the impedance of the
combined signal of the receiver 20 to the impedance required by the
rest of the RX resonator array 21 circuitry (i.e., rectifier,
regulator) such that optimum charging conditions (current, voltage)
are created at the charging device or load (such as a battery).
[0048] In some embodiments, the receiver 20 further includes a
communication module to transmit feedback information so that the
transmitter configures its phases to generate the near zone
magnetic field optimized to the receiver.
[0049] The transmitter 10 and the receiver 20 stated above can be
used together to maximize the efficiency of power transfer.
However, the transmitter 10 can also be used with other types of
receive resonators, such as a single receive resonator (#M=1). The
receiver 20 also can be used with the other types of transmit
resonators, such as a single transmit resonator (#N=1). In some
embodiment, an intermediate loop resonator can be located between
the transmitter 10 and receiver 20 to relay the near zone magnetic
field at longer ranges.
Linear Polarization Mode
[0050] FIG. 3 schematically illustrates the transmitter 10 and the
receiver 20 operating under the linear polarization mode according
to one embodiment of the present disclosure. A linearly polarized
transmitter 10 can be implemented either by a single resonator with
one excitation port (one sub-signal), or a resonator array with
multiple in-phase excitation ports (i.e., zero delay or phase
difference between sub-signals).
[0051] In the case of a linearly polarized transmitter 10 comprised
of a resonator array 18 with #M resonators, all resonators are
transmitting in phase (i.e., zero phase difference between
sub-signals), and power is able to or not to be uniformly
distributed among the array elements, hence the excitation
coefficients A.sub.1 . . . A.sub.M.
[0052] A linearly polarized transmitter 10 has no control of the
phase of the current on the resonator structure, and produces
equivalent linearly polarized magnetic fields. A linearly polarized
field can be expressed over time at a fixed location in space, say
r=r0 as follows:
{right arrow over (H)}(r=r.sub.0,t)={right arrow over (H)}.sub.0
cos(.omega.t) (3)
[0053] FIG. 4 depicts how the magnetic field vector oscillates at a
fixed location in space, say r=r0, and at different time instances.
As seen, the vector oscillates on a straight line but at different
orientations depending on the location around the resonator, as
shown in FIG. 3.
[0054] A linearly polarized receive resonator 20 can have a single
resonator with one excitation port, or a resonator array with
multiple in-phase excitation ports. In the case that a linearly
polarized receiver includes a resonator array with #M resonators,
the phase difference between all resonators is set to zero (i.e.,
resonators are receiving in phase).
[0055] Referring back to FIG. 3, the resonators Rx.sub.1 and
Rx.sub.2, where the magnetic field vector is parallel to the
surface normal of resonators, are optimally oriented for maximum
mutual coupling with a transmitter. As the Rx unit is rotated at an
angle .phi. at a particular Rx location, away from the optimum
orientation, the mutual coupling will drop proportionally to the
cosine of the rotation angle T, causing detuning of the resonant
coupling and drop in the coupling efficiency. As the worst case,
resonators Rx.sub.3 and Rx.sub.4 where the surface normal of the Rx
resonator is perpendicular to the magnetic field H at the location
of the Rx, have zero coupling with a transmitter, thus do not
receive any power.
[0056] In some embodiments, the resonator array Rx.sub.5, still
linearly polarized, can include multiple resonators, thus multiple
ports, disposed at various orientations. Each resonator might or
might not be favorably positioned depending on its orientation, and
similar degradation in mutual coupling will occur with changes in
orientation.
Elliptical Polarization Mode
[0057] FIG. 5 schematically illustrates the transmitter 10 and the
receiver 20 operating under the elliptically polarized mode
according to one embodiment of the present disclosure.
[0058] In the embodiment, the transmitter 10 includes a Tx
resonator array 18 comprised of #M resonators. Each Tx resonator
produces a magnetic field corresponding to the sub-signal with the
weighing coefficient Ai and the phase .theta.i (i=1 . . . M). The
magnetic fields generated from the #M resonators are combined to
form the near zone magnetic field. The resonators of the resonator
array 18 may or may not be electrically interconnected.
[0059] The transmitter 10 can control the polarization of near
magnetic field by adjusting weighing coefficients A.sub.1, . . . ,
A.sub.M and the phases .theta..sub.1, . . . , .theta..sub.M. In
other words, providing appropriate values of A.sub.1, . . . ,
A.sub.M and .theta..sub.1, . . . , .theta..sub.M, the near zone
magnetic field H can be circularly or elliptically polarized, and
thus rotate with time. Further, by forcing the near zone magnetic
field {right arrow over (H)} to rotate, the transmitter enables
power transfer via mutual inductance to the receivers for at least
a portion of the cycle of rotation, independent of position or
orientation around the Tx resonator.
[0060] An elliptically polarized magnetic field formed from two
unit magnetic fields Hx, Hy can be expressed over time at a fixed
location in space, say r=r.sub.0 as follows:
{right arrow over (H)}(r=r.sub.0,t)={right arrow over (H)}.sub.x
cos(.omega.t+.phi..sub.x)+{right arrow over (H)}.sub.y
cos(.omega.t+.phi..sub.y) (4)
[0061] As shown in FIG. 6, at a fixed location in space, say
r=r.sub.0, the tip of the field vector traces an ellipse located on
a specific plane. Depending on the magnitude and phase of the
components H.sub.x and H.sub.y, polarization turns into circular,
elliptical or linear. Specifically, the polarization of the near
zone magnetic field becomes: circular when H.sub.x and H.sub.y are
equal in magnitude and the phase difference between them is
.phi..sub.x-.phi..sub.y=odd multiples of .pi./2; linear if the
phase difference between them is .phi..sub.x-.phi..sub.y=multiples
of .pi.; and in all other cases elliptical. The phase shifts of
each resonator can be predetermined or adjusted with respect to the
shape of near zone magnetic field polarization. In some
embodiments, the transmitter receives feedback information to
configure the phases of each resonator so as to generate the near
zone magnetic field optimized to the receiver.
[0062] It should be noted that x and y do not necessarily refer to
the usual Cartesian coordinates, but rather to the exactly two
perpendicular components {right arrow over (H)}.sub.x and {right
arrow over (H)}.sub.y, necessary to express the polarization of any
resonator at the near-field. Further, if the sub-signals fed into
the multiple loop resonators have different resonance frequencies
.omega..sub.1, .omega..sub.2, the polarization of the total
magnetic field can be also controlled.
[0063] The receiver 20 under the elliptically polarized mode can
include a single resonator, such as cases Rx.sub.1 to Rx.sub.4, or
a resonator array 21, such as Rx.sub.5, comprised of multiple
resonators configured such that they can receive substantially
perpendicular magnetic fields. In the case of the resonator array
21, the sub-signals received by the array resonators are delayed or
phased with angles .phi.1 . . . , .phi.n.
[0064] Referring back to FIG. 4, Rx resonators Rx.sub.1 to Rx.sub.4
are linearly polarized while resonator Rx.sub.5 is elliptically
polarized. Forcing the near zone magnetic field {right arrow over
(H)} to rotate by appropriately adjusting the delay or phases of
the Tx resonators, enables power transfer via mutual inductance to
all receivers, independent of position or orientation around the Tx
resonator. The Rx resonators can either be linearly polarized such
as resonators Rx.sub.1 to Rx.sub.4, or elliptically polarized, such
as Rx.sub.5. All Rx.sub.1 to Rx.sub.4 receivers can be favorably
positioned for some part of the cycle, and thus with proper design
mutual inductance can stay at stable levels independent of the
receiver resonator's orientation. In other embodiments, receiver
Rx.sub.5 can be designed to be circularly or elliptically
polarized.
[0065] The phase shifts of each receive resonator can be
predetermined with respect to polarization of the near zone field.
Alternatively, using numerical optimization and circuit analysis,
the required phase shifts can be found for each resonator so as to
obtain stable mutual inductance M between the transmit and receive
resonators, for a wide range of orientation angles.
[0066] In some embodiments, the receiver 20 transmits feedback
information for the transmitter 10 to configure the phases of the
transmit resonator array 18 so as to generate the near zone
magnetic field optimized to the receiver.
[0067] FIG. 7 illustrates an elliptically polarized resonator 40
array according to one embodiment of the present disclosure. As
shown in FIG. 7, the resonator array includes three loop
resonators, each resonator of which being substantially
perpendicular to and overlaid on portions of one another.
Accordingly, the three magnetic fields generated by three
resonators are substantially orthogonal to one another in the near
zone. The loops can be a number of different shapes (e.g.,
circular, elliptical, square, and rectangular). Also, the loops can
be in wide variety of sizes. As stated above, each of three
resonators is fed with sub-signal with a weighing coefficient Ai
and a phase .theta.i and produces magnetic fields corresponding to
a fed sub-signal.
[0068] The term "substantially orthogonal" as herein to describe
the placement of loop resonators refers to the state that the
directions of the magnetic field vectors generated by at least two
loop resonators cross one another to generate a polarized magnetic
field, such as an elliptically, circularly or linearly polarized
magnetic field. The range of degrees between two magnetic field
vector directions in order to be "substantially orthogonal" is from
15.degree. to 165.degree..
[0069] In some embodiments where the resonator array is adopted for
a transmitter, the transmitter can be used to produce elliptically
or linearly polarized magnetic field by adjusting weighing
coefficients Ai and phases .theta.i. In other embodiments, where
the resonator array is adopted for a receiver, the receiver can
maximize received power by adjusting the phases .phi.i.
[0070] The resonant frequency of the loop resonator is based on the
closed loop inductance and an externally added capacitance.
Inductance in a loop resonator is generally the inductance created
by the loop, whereas, capacitance is generally added externally to
the loop resonator's inductance to create a resonant structure at a
desired resonant frequency.
[0071] FIG. 8 illustrates exemplary phase shift circuits according
to embodiments of the present disclosure. As stated above, the
phase shifters are coupled to Tx and Rx resonators and provides
each resonator with the appropriate phases .theta..sub.1, . . . ,
.theta..sub.M, and .phi..sub.1, . . . , .phi..sub.N to rotate the
near zone magnetic field or to optimize Rx resonator to receive
maximum power from that near zone magnetic field.
[0072] At low frequencies (i.e., the physical size and length of
the resonator is much smaller than the operating wavelength) and
for narrow bandwidths, such as that allocated for wireless power
transfer, phase shifters can be implemented via low/high pass
filters. The design of such filters can be guided using the
lossless circuits and their corresponding equation as follows:
L 1 = Z 0 1 - cos .PHI. .omega. sin .PHI. , C 1 = sin .PHI. .omega.
Z 0 for ( a ) ( 5 ) L 2 = Z 0 .omega. sin .PHI. , C 2 = sin .PHI.
.omega. Z 0 ( 1 - cos .PHI. ) for ( b ) ( 6 ) L 3 = Z 0 sin .PHI.
.omega. , C 3 = ( 1 - cos .PHI. ) .omega. Z 0 sin .PHI. for ( c ) (
7 ) L 4 = Z 0 sin .PHI. .omega. ( 1 - cos .PHI. ) , C 4 = 1 .omega.
Z 0 sin .PHI. for ( d ) ( 8 ) ##EQU00003##
where, .phi. is the desired phase difference or delay at the
specified frequency .omega., and Z.sub.0 is the characteristic
impedance of the system.
[0073] The choice of the appropriate phase shifter topology is
based on the availability of the components, the availability of
space on the resonator device, the loss performance of the
available components, and the like. In some embodiments, the phase
shifter can be designed based on equations 5 to 8. Alternatively,
an optimization method regarding the phase shift value can employed
for best performance. Currently, standardization of wireless power
transfer systems allows operation at the ISM frequency bands (6.78
MHz and 13.56 MHz with 15 KHz bandwidth). The choice of these
frequencies relates to various reasons, however, from an
electromagnetic standpoint there is no particular restriction in
the choice of the operation frequency, as long as the near-field
condition is satisfied.
Demonstration of Orientation-Free Wireless Power Transfer
[0074] FIG. 9 illustrates a wireless transfer system using a
transmit and receive resonators according to one embodiment of the
present disclosure. The resonators include two orthogonally placed
circular loops, 32 cm in diameter, and the two loops are fed with
equal power via a T-junction. The receive resonator array is
statically rotated around itself at angles .phi.
[0.degree.,180.degree.] and the operation frequency is 6.78
MHz.
[0075] Using circuit analysis we found the required phase shift for
each resonator so as to obtain stable mutual inductance M between
the transmit and receive resonators, for a wide range of rotation
angles. The equivalent circuit parameters for the Tx and Rx
resonator are as follows:
L.sub.Tx=69nH,L.sub.RX=413nH,R.sub.Tx=0.066.OMEGA.,R.sub.Rx=0.052.OMEGA.
(9)
.PHI..sub.1=180.degree.,.PHI..sub.2=0.degree.,.theta..sub.1=31.degree.,.-
theta..sub.2=0.degree. (10)
[0076] In the embodiment, the mutual inductance M of the system of
resonators with and without the use of phase shifters is depicted
in FIG. 10. As shown in FIG. 10, the use of phase shifters leads to
a stable mutual inductance of 2.5 nH for rotation angles ranging
from 20.degree.-100.degree.. On the contrary, if no phase shifters
are used, mutual inductance exhibits large variations which lead to
system detuning and loss of efficiency. It should be noted that the
use of phase shifters at these low frequencies does not practically
increase the system complexity or cost.
[0077] The embodiments of the present disclosure would provide
methods and apparatuses that enable efficient wireless three
dimensional (3D) power transfer independent of the relative
position and orientation of a transmitter and a receiver.
[0078] Although the present disclosure has been described with an
exemplary embodiment, various changes and modifications may be
suggested to one skilled in the art. It is intended that the
present disclosure encompass such changes and modifications as fall
within the scope of the appended claims.
* * * * *